I kept hearing a clicking sound from the front of my bike and couldn't figure out where it was coming from. It was the same speed as a piece of gravel stuck in the tread, but I couldn't find anything. It sounded more metallic but I couldn't find anything by the spokes. It'd come and go. Finally one day I stopped on the way home and thought I better get to the bottom of it.
Searched the bike and found the sound was coming from the rear, not the front:
I can't believe I rode around like this for days. I picked up a staple somewhere and one end was hitting the chainstay every tire revolution. The other end must've just missed the tube or not punctured far enough in. I waited til I got home before removing it, just in case I managed to give myself a flat while pulling out the staple. My new philosophy towards flats is "you're gonna get them so don't sweat 'em", but I gotta admit I was relieved I didn't have to fix a flat.
My total guesstimate on the causes of flats on the streets of Spokane:
Unexplained by natural causes therefore must be some mysterious flat force field: 13% (Einstein was rumored to be working on an all-encompassing unified flat field theory in his later years.)